1. Field of the Invention
The present invention relates to an image processing apparatus, and more particularly to an image processing apparatus which stores input image data into a memory to effect image processing.
2. Related Background Art
In a prior art image processing apparatus such as a facsimile apparatus, a system for storing image data into a memory before it is transmitted or outputted for recording has been known.
Compression of the image data to shorten an image transmission/reception time has also been known.
Data compression is useful to reduce memory capacity for storing the image data. Methods of storing the image data include, storing uncompressed raw data or storing the image data in a compressed form by a coding system such as an MH (modified Huffman) code or an MR (modified READ) code.
United State Patent (USP) relating to a facsimile apparatus which stores image data into a memory include U.S. Pat. Nos. 4,717,967, 4,796,092, 4,677,649, 4,814,890, 4,772,955 and 4,845,569.
When the image data is stored in prior art image processing apparatus, it is common to store the image data as raw image data or compressed data such as MH code or MR code. However, prior art methods have the following disadvantages.
(1) Storing by the raw image data only
Since the data volume for one sheet (one page) of the binarized image is constant whether the compression factor is high or low, an assured number of pages to be stored can be determined from the memory capacity, and it is a maximum number of sheets (pages) to be stored.
Where the assured number of pages to be stored is to be increased, a considerable memory capacity is required and a cost significantly increases.
(2) Storing by compressed code data only such as MH code or MR code:
Since the MH or MR code for compression is determined based on a statistical nature of a most popular image such as a text document, the compression factor of the image data is low for a document image having a different statistical nature, and the volume after the compression may be several times as large as that of the raw image data. As a result, the assured number of pages to be stored cannot be determined, and the number of sheets to be stored depends on the document and is very unstable.